How do you call a payable method from the js client?

Question

Imagine you got a smart contract method that expects a deposit attached to a method call, something like this rust method:

#[payable]
pub fn spend(&mu self, age: u8){
    assert!(env::attached_deposit() > 0,
            "Insufficient deposit.");
.
.
.
}

now you setup your contract using near-api-js and proceed to call it. How can one call this method and attach some Near to it in the client side js?

Answer 1

You set up your contract as usual:

const contract = await new nearlib.Contract(
    walletConnection.account(),
    nearConfig.contractName,
    {
      // View methods are read only. They don't modify the state, but usually return some value.
      viewMethods: ["getCorgi", "getCorgisList", "displayGolbalCorgis"],
      // Change methods can modify the state. But you don't receive the returned value when called.
      changeMethods: ["transferCorgi", "createCorgi", "deleteCorgi"],
      // Sender is the account ID to initialize transactions.
      sender: walletConnection.getAccountId(),
    }
  );

Usually, you call change methods as:

await contract.transferCorgi({"receiver": "frol.near", "id": "corgi_xxx", "message": "hello"})

However, when you want to attach some NEAR tokens or increase gas allowance, you need to specify optional positional arguments after the arguments:

await contract.changeMethodName(args: object, gas: BN, amount: BN)

NOTES:

0. BN is a big number representation
1. the default gas allowance is 300 Tgas [300 * 10^12 gas], learn more: FAQ on Gas in the documentation, NEP67
2. amount is specified in yoctoNEAR (1 NEAR is 10^24 yoctoNEAR)

For example:

const ONE_NEAR = new BN("1000000000000000000000000")
await contract.createCorgi({"id": "corgi_xxx"}, new BN("3000000000000"), ONE_NEAR)